In-vehicle power supply device

ABSTRACT

The present disclosure aims to avoid a situation where a drive unit to be used for precharge does not drive due to a drop in power supply voltage. The power supply device is provided with the first voltage conversion unit and the control unit. The first voltage conversion unit performs a third voltage conversion operation in which a voltage applied to a second conductive path is boosted and an output voltage is output to a first conductive path to which a capacitive component is electrically connected. The control unit supplies the third control signal to only some of the plurality of first voltage conversion units, thereby causing the some of the first voltage conversion units to perform the third voltage conversion operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of PCT/JP2019/019070 filedon May 14, 2019, which claims priority of Japanese Patent ApplicationNo. JP 2018-099742 filed on May 24, 2018, the contents of which areincorporated herein.

TECHNICAL FIELD

The present disclosure relates to an in-vehicle power supply device.

BACKGROUND

In vehicles provided with a rechargeable battery, when for example theignition is turned off, the rechargeable battery is separated from anyload connected to the battery and put into standby in some cases, inorder to curb current consumption of the rechargeable battery. In thisstandby state, charges accumulated in capacitive components in this loadare discharged, and the difference between a terminal voltage of therechargeable battery and the voltage of the load increases. When therechargeable battery is connected to this load in a state where thedifference between the terminal voltage of the rechargeable battery andthe voltage of the load is great, a large inrush current is generatedbetween the rechargeable battery and the load.

A technique as disclosed in JP 2017-22805A has been proposed as atechnique for solving this kind of problem. In the technique disclosedin JP 2017-22805A, before connecting the rechargeable battery and theload, by precharging a capacitive component in the load using a boostDC-DC converter, the generation of a large inrush current between therechargeable battery and the load is curbed.

Incidentally, in order to perform precharge using a DC-DC convertor, aswitching element that serves as a main element that performs a voltageconversion operation needs to be driven by a driver, and for thispurpose, power needs to be supplied to the driver. On the other hand, inrecent years, in order to reach the performance required for DC-DCconverters, a configuration is used in which a plurality of switchingelements are arranged in parallel, and the converters are connected inparallel to increase the number of phases. Due to such an increasedparallelization, the current (drive current) that is output to theswitching element and the like via the driver tends to increase. As aresult of this, a more significant voltage drop tends to occur inresistive components, diode components, and the like, which are arrangedin a path between the driver and a power supply that supplies power tothe driver. Accordingly, if the power supply voltage (voltage of powersupply for supplying power to the driver) drops, the voltage (thresholdvoltage) required for the operation of the driver may not be reached.

The present disclosure has been made in order to solve at least one ofthe above-described problems, and aims to realize an in-vehicle powersupply device that can reduce the changes that a control unit receivingpower supplied from a power supply cannot perform control of a prechargeoperation even if the power supply voltage drops.

SUMMARY

A first aspect of the present disclosure is an in-vehicle power supplydevice configured to lower a voltage applied to a first conductive paththat is electrically connected to a capacitive component and apply theresultant voltage to a second conductive path, or boost a voltageapplied to the second conductive path and apply the resultant voltage tothe first conductive path. The in-vehicle power supply device includes afirst voltage conversion unit that includes a first drive switchingelement, a second drive switching element, and a first inductor. Thefirst voltage conversion unit performs a first voltage conversionoperation in which a voltage applied to the first conductive path islowered and an output voltage is applied to the second conductive path,in accordance with a first control signal, in which an ON signal and anOFF signal are alternately switched, being supplied to the first driveswitching element, and performs a third voltage conversion operation inwhich a voltage applied to the second conductive path is boosted and anoutput voltage is applied to the first conductive path in accordancewith a third control signal, in which an ON signal and an OFF signal arealternately switched, being supplied to the second driving switchingelement. A reverse-flow prevention switching element is provided on thesecond conductive path and interrupts a flow of a current on the secondconductive path toward the first voltage conversion unit when turnedOFF. A second inductor is provided between the first voltage conversionunit and the reverse-flow prevention switching element on the secondconductive path, and in series with respect to the reverse-flowprevention switching element. A semiconductor element part constitutedby a diode or a switching element that has one end electricallyconnected to the second inductor and the reverse-flow preventionswitching element on the second conductive path and another endelectrically connected to a reference conductive path. A control unitoutputs the first control signal to at least the first drive switchingelement, and outputs the third control signal to the second driveswitching element, in which a plurality of the first voltage conversionunits are connected in parallel with each other between the firstconductive path and the second conductive path. A second voltageconversion unit is configured by including the reverse-flow preventionswitching element, the second inductor, and the semiconductor elementpart, and, when a part of the second conductive path that is on thefirst voltage conversion unit side of the second voltage conversion unitis regarded as an output-side conductive path, and a part of the secondconductive path that is on the side opposite to the first voltageconversion unit side is regarded as an input-side conductive-path. Thesecond voltage conversion unit performs the second voltage conversionoperation in which the voltage applied to the input-side conductive pathis lowered, and an output voltage is applied to the output-sideconductive path, the control unit being configured to cause the secondvoltage conversion unit to perform the second voltage conversionoperation in accordance with a predetermined precharge condition beingsatisfied, by applying a second control signal, in which an ON signaland an OFF signal are alternately switched, to the reverse-flowprevention switching element, and upon starting the second voltageconversion operation. The control unit supplies the third control signalto only some of the plurality of the first voltage conversion units inaccordance with a predetermined switching condition being fulfilled,thereby causing some of the first voltage conversion units to performthe third voltage conversion operation.

Advantageous Effects of Disclosure

According to an in-vehicle power supply device according to the firstaspect, since the second voltage conversion unit can be caused toperform the second voltage converting operation in accordance with apredetermined precharge condition being fulfilled, if the switch unit isswitched from the OFF state to the ON state at least after the secondvoltage conversion operation is performed in this manner, the switchunit is switched from the OFF state to the ON state in a state wherecharging of the capacitive component progresses to some extent.Accordingly, it is possible to suppress an inrush current that flowsinto the capacitive component from the first power supply unitimmediately after the switching.

In addition, if a predetermined condition is fulfilled in the secondvoltage conversion operation, it is possible to perform the thirdvoltage conversion operation such that the voltage applied to the secondconductive path is boosted and the resultant voltage is applied to thefirst conductive path, and thus the charging of the capacitive componentconnected to the first conductive path side can progress further.

In addition, with a configuration, in which only some of the firstvoltage conversion units are caused to perform the third voltageconversion operation by supplying the third control signal to only someof the first voltage conversion units among the plurality of firstvoltage conversion units in a case where the control unit causes thefirst voltage conversion unit to perform the third voltage convertingoperation when a predetermined switching condition is fulfilled, it ispossible to reduce the power that is required for the control unit todrive the first voltage conversion unit during the third voltageconversion operation. Accordingly, even if the voltage of the powersupply that supplies power to the control unit drops, a situation wherethe control unit cannot perform control of the precharge operation(control of the third voltage converting operation) is not likely tooccur.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically illustrating a configuration ofan in-vehicle power supply system including an in-vehicle power supplydevice of a first embodiment.

FIG. 2 is a block diagram specifically illustrating a configuration of avoltage conversion device included in the in-vehicle power supplydevice.

FIG. 3 is a flowchart illustrating an operational flow of prechargeperformed by a control unit included in the in-vehicle power supplydevice.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The in-vehicle power supply device according to the present disclosuremay also include a plurality of third conductive paths that serve as apower supply path from the second conductive path to the control unit.Furthermore, the plurality of third conductive paths may also beconnected in parallel with each other between the second conductive pathand the control unit, and a voltage generation unit that boosts avoltage applied to the conductive path on the second conductive pathside and applies the output voltage to the conductive path on thecontrol unit side may also be provided on one of the third conductivepaths.

According to this configuration, even if the voltage applied to thesecond conductive path is small, the voltage generation unit can boostthe voltage applied to the conductive path on the second conductive pathside and apply the output voltage to the conductive path on the controlunit side. Accordingly, even if the voltage applied to the secondconductive path is small, the drive voltage required for the operationof the control unit is readily ensured.

Furthermore, in the in-vehicle power supply device according to thepresent disclosure, the control unit may also output the control signalto only one of the plurality of the voltage conversion units in thethird voltage conversion operation.

With this configuration, since the number of switching elements thatdrive can be minimized, also the power consumed by the drive unit thatgenerates the control signal for controlling the drive switchingelements can be minimized.

Upon starting the second voltage conversion operation, the control unitmay also supply the third control signal to only one first voltageconversion unit of the plurality of first voltage conversion units inaccordance with a predetermined switching condition being fulfilled,thereby causing the one first voltage conversion unit to perform thethird voltage conversion operation.

With this configuration, the power required for the control unit todrive the first voltage conversion unit during the third voltageconversion operation can be further reduced. Accordingly, even if thevoltage of the power supply for supplying the control unit drops, asituation where the control unit cannot perform the control of aprecharge operation (control of the third voltage conversion operation)is less likely to occur.

First Embodiment

The following describes a first embodiment, which is a specific exampleof the present disclosure.

An in-vehicle power supply device 1 (hereinafter also referred to as“power supply device 1”) of the first embodiment is a part of anin-vehicle power supply system 100 (hereinafter also referred to as“power supply system 100”) shown in FIG. 1 . The power supply system 100includes a first power supply unit 90, a second power supply unit 92, afirst load 94, a second load 96, and a power supply device 1, forexample. The power supply system 100 is configured as a system that cansupply power to the first load 94 using the first power supply unit 90as the power supply source, and charge (precharge) a capacitivecomponent of the first load 94 that has discharged when turning OFF anignition switch or the like via the power supply device 1, using thesecond power supply unit 92 as the power supply source.

The first power supply unit 90 is a part that can supply power to thefirst load 94 or the second load 96, and is configured as a knownin-vehicle battery such as a lithium ion battery. In the first powersupply unit 90, a high-potential terminal is electrically connected tothe first conductive path 10 and a low-potential terminal iselectrically connected to a reference conductive path (ground part, notshown), and a predetermined output voltage is applied to the firstconductive path 10. When the switch unit 98 provided on the firstconductive path 10 is switched from an OFF state to an ON state, thefirst power supply unit 90 is electrically connected to the first load94 and the power supply device 1 via the first conductive path 10.

The second power supply unit 92 is a part that can supply power to thefirst load 94 or the second load 96, and is configured as a knownin-vehicle battery such as a lead battery. In the second power supplyunit 92, a high-potential terminal is electrically connected to thesecond conductive path 12 and a low-potential terminal is electricallyconnected to the ground part (not shown), and a predetermined outputvoltage is applied to the second conductive path 12. The second powersupply unit 92 is electrically connected to the second load 96 and thepower supply device 1 via the second conductive path 12.

The first load 94 includes a capacitive component, and this capacitivecomponent corresponds to an example of the capacitive component of thepresent disclosure. The first load 94 is electrically connected to thefirst conductive path 10, and is connected to the power supply device 1via the first conductive path 10. The capacitive component may be acapacitor or the like, or any other capacitive component.

The second load 96 includes a capacitive component. The second load 96is electrically connected to the second conductive path 12, and isconnected to the power supply device 1 via the second conductive path12.

The power supply device 1 is configured as a device that can lower avoltage applied to the first conductive path 10 and apply the resultantvoltage to the second conductive path 12, and also boost or lower avoltage applied to the second conductive path 12 and apply the resultantvoltage to the first conductive path 10. The power supply device 1includes a first voltage detection unit 80, a first current detectionunit 84, a second voltage detection unit 82, a second current detectionunit 86, a voltage conversion device 20, and a control unit 88, forexample.

The first voltage detection unit 80 is configured as a known voltagedetector, for example, and detects and outputs the voltage of the firstconductive path 10. Specifically, the first voltage detection unit 80detects the voltage output from the power supply device 1 to the firstload 94 and outputs a value reflecting the detected (output) voltage(e.g., the exact value or a voltage-divided value of the voltage of thefirst conductive path 10) as the detected value.

The first current detection unit 84 is configured as a known currentdetector, for example, and detects and outputs the current output fromthe power supply device 1 to the first load 94. Specifically, the firstcurrent detection unit 84 includes a resistor that is arranged on thefirst conductive path 10, and a differential amplifier. The voltagebetween the two ends of the resistor is input to the differentialamplifier, the voltage drop generated in the resistor due to the currentflowing through the first conductive path 10 is amplified by thedifferential amplifier, and the resultant value is output as thedetected value.

The second voltage detection unit 82 is configured as a known voltagedetector, for example, and detects and outputs the voltage of the secondconductive path 12. Specifically, the second voltage detection unit 82detects a voltage output from the power supply device 1 to the secondload 96 and outputs the value reflecting the detected (output) voltage(e.g., the exact value or a voltage-divided value of the voltage of thesecond conductive path 12) as the detected value.

The second current detection unit 86 is configured as a known currentdetector, for example, and detects and outputs the current flowingthrough the second conductive path 12. Specifically, the second currentdetection unit 86 includes a resistor that is arranged on the secondconductive path 12, and a differential amplifier. The voltage betweenthe two ends of the resistor is input to the differential amplifier, thevoltage drop generated in the resistor due to the current flowingthrough the second conductive path 12 is amplified by the differentialamplifier, and the resultant value is output as the detected value.

The voltage conversion device 20 includes a plurality of first voltageconversion units 21 provided in parallel with each other, and isconfigured as a multiphase DC-DC convertor that can operate usingsynchronous rectification. One end of the voltage conversion device 20is electrically connected to the first conductive path 10, and the otherend is electrically connected to the second conductive path 12. Thevoltage conversion device 20 can lower the voltage applied to the firstconductive path 10 and apply the resultant voltage to the secondconductive path 12, and can boost the voltage applied to the secondconductive path 12 and apply the resultant voltage to the firstconductive path 10.

The control unit 88 is a part that controls the operation of the voltageconversion device 20, and is constituted by mainly including a controlcircuit, first drive units 50, and a second drive unit 32. In thecontrol unit 88, the control circuit is configured as a microcomputer,for example, and includes a computation device such as a CPU, a memorysuch as a ROM or a RAM, an AD convertor, and the like. Power is suppliedto the control unit 88 from the first power supply unit 90 or the secondpower supply unit 92.

The control unit 88 is electrically connected to the first voltagedetection unit 80, the second voltage detection unit 82, the firstcurrent detection unit 84, and the second current detection unit 86, andcan obtain the detected values of these detection units. The controlunit 88 has a function of determining a duty ratio based on the obtaineddetected value, and generating and outputting a PWM signal with thedetermined duty ratio. The control unit 88 can control the plurality offirst voltage conversion units 21 individually by generating a PWMsignal SG1 and outputting the PWM signal SG1 to the first drive units 50provided in each of the first voltage conversion units 21. In thismanner, the control unit 88 can perform control such that the firstvoltage conversion units 21 (voltage conversion device 20) boost orlower the voltage.

As shown in FIG. 2 , the power supply device 1 includes the plurality offirst voltage conversion units 21, a plurality of reverse-flowprevention switching elements 24, a second inductor 26, a switchingelement 28, a capacitor 30, the second drive unit 32, and a signalgeneration circuit 34, for example.

The plurality (all) of first voltage conversion units 21 are provided inparallel with each other. The first voltage conversion units 21 are eachconfigured as a synchronous rectification-type step up/down DC-DCconvertor, and can perform a first voltage conversion operation in whichthe voltage applied to the first conductive path 10 is lowered and theresultant voltage is applied to the second conductive path 12.Furthermore, one end of each first voltage conversion unit 21 iselectrically connected to the first conductive path 10, and the otherend is electrically connected to the second conductive path 12.

The first voltage conversion units 21 are each provided with a high-sideswitching element 40, a low-side switching element 42, and a firstinductor 44. The switching element 40 is configured as an N-channelMOSFET, and the first conductive path 10 is electrically connected tothe drain of the switching element 40, and the drain of the switchingelement 42 and one end of the first inductor 44 are connected to thesource thereof. The drain of the switching element 42 is connected tothe connection point of the switching element 40 and the first inductor44. The source of the switching element 42 is electrically connected tothe reference conductive path. Note that the switching element 40corresponds to an example of the first drive switching element. Theswitching element 42 corresponds to an example of the second driveswitching element.

The first voltage conversion units 21 each have a high-side capacitor 46and a low-side capacitor 48. One end of the capacitor 46 is connected tothe first conductive path 10, and the other end is electricallyconnected to the reference conductive path. One end of the capacitor 48is connected to the second conductive path 12, and connected to theother end of the first inductor 44 and one end of the second inductor 26via the second conductive path 12. The other end of the capacitor 48 iselectrically connected to the reference conductive path.

The plurality of first drive units 50 are respectively provided to theplurality of first voltage conversion units 21. The first drive units 50correspond to an example of the drive unit, and apply, to the gate ofthe switching elements 40 and 42, an ON signal (PWM signal) foralternately turning ON the switching elements 40 and 42, based on thePWM signal SG1 generated by the control unit 88. Note that the PWMsignal that is output to the switching elements 40 by the first driveunit 50 when performing a voltage drop operation corresponds to anexample of a first control signal. Hereinafter, the PWM signal that isoutput to the switching elements 40 and 42 by the first drive unit 50 isalso referred to as “control signal”.

The plurality (all) of reverse-flow prevention switching elements 24 arearranged such that a plurality of semiconductor switching elements 24A,24B, 24C, . . . and so on are connected in parallel with each other. Thereverse-flow prevention switching elements 24 have a function ofinterrupting a current flowing into the first voltage conversion units21 on the second conductive path 12 when all the semiconductor switchingelements 24A, 24B, 24C, . . . and so on are turned OFF. Specifically,the plurality of semiconductor switching elements 24A, 24B, 24C, . . .and so on are each configured as an N-channel MOSFET, and the drainsthereof are electrically connected to the conductive path of the secondconductive path 12 on the second power supply unit 92 side, and thesources thereof are electrically connected to the conductive path of thesecond conductive path 12 on the first voltage conversion unit 21 side.

The second inductor 26 is provided between the first voltage conversionunit 21 and the reverse-flow prevention switching elements 24 on thesecond conductive path 12, and provided in series with the reverse-flowprevention switching elements 24. Specifically, one end of the secondinductor 26 is electrically connected to the connection points of thefirst inductors 44 and the capacitors 48 of the first voltage conversionunits 21, and the other end is electrically connected to the sources ofthe reverse-flow prevention switching elements 24 and the drain of theswitching element 28.

The switching element 28 corresponds to an example of a semiconductorelement part, and is configured as a MOSFET, for example. The drain (oneend) of the switching element 28 is electrically connected between thesecond inductor 26 and the reverse-flow prevention switching elements 24on the second conductive path 12, and the source (the other end) thereofis electrically connected to the reference conductive path.

One end of the capacitor 30 is connected to the second conductive path12 on the second power supply unit 92 side of the reverse-flowprevention switching elements 24, and the other end is electricallyconnected to the reference conductive path.

In this configuration, the second voltage conversion unit 22 isconstituted by the reverse-flow prevention switching elements 24, thesecond inductor 26, and the switching element 28 (semiconductor elementpart). This second voltage conversion unit 22 constitutes a synchronousrectification-type step up/down DC-DC convertor. The second conductivepath 12 includes an output-side conductive path 12B on the first voltageconversion unit 21 side of the second voltage conversion unit 22, andincludes an input-side conductive path 12A on the opposite side of thefirst voltage conversion unit 21. The second voltage conversion unit 22can perform a second voltage conversion operation in which the voltageapplied to the input-side conductive path 12A is lowered and the outputvoltage is applied to the output-side conductive path 12B.

The second drive unit 32 applies, to the gates of reverse-flowprevention switching elements 24 and the switching element 28, an ONsignal (PWM signal) for alternately turning ON the reverse-flowprevention switching elements 24 and switching element 28, based on thePWM signal SG2 generated by the control unit 88. Note that the PWMsignal that is output from the second drive unit 32 to the reverse-flowprevention switching elements 24 corresponds to an example of a secondcontrol signal. Hereinafter, the PWM signal output from the second driveunit 32 to the reverse-flow prevention switching element 24 is alsoreferred to as “control signal”.

Furthermore, of the plurality of reverse-flow prevention switchingelements 24, the gate of some (in the first embodiment, one) of thereverse-flow prevention switching elements 24A is directly supplied withthe control signal from the second drive unit 32, and anotherreverse-flow prevention switching element 24B is supplied with thecontrol signal from the second drive unit 32 via the signal generationcircuit 34.

The signal generation circuit 34 is provided between the second driveunit 32 and the gate of the reverse-flow prevention switching element24B. The signal generation circuit 34 interrupts the control signal thatis output from the second drive unit 32 to the reverse-flow preventionswitching element 24B based on an interruption instruction signal SG3that is output from the control unit 88.

Third conductive paths 60 are respectively provided between the secondconductive path 12 and the first drive unit 50 and between the secondconductive path 12 and the second drive unit 32. The third conductivepaths 60 are configured such that parts thereof are arranged inparallel, one conductive path arranged in parallel is provided with adiode 62, and the other conductive path is provided with a diode 64 anda voltage generation unit 66. The anode of the diode 62 is connected tothe second conductive path 12, and the cathode is connected to the firstdrive unit 50 and the second drive unit 32. The voltage generation unit66 is connected to the diode 64 in series, and provided on the secondpower supply unit 92 side of the diode 64. The anode of the diode 64 isconnected to the voltage generation unit 66, and the cathode isconnected to the first drive unit 50 and the second drive unit 32. Thevoltage generation unit 66 is configured as a boosting circuit, forexample, and can boost the voltage input from the second conductive path12 side and output the resultant voltage to the first drive unit 50 andthe second drive unit 32 side, based on a boost instruction signal SG4from the control unit 88.

Next, the operation of the power supply device 1 will be explained.

When switching the switch unit 98 from the OFF state to the ON state tosupply power from the first power supply unit 90 to the first load 94,the power supply device 1 can perform an operation for charging inadvance (precharging) the capacitive component of the first load 94using power from the second power supply unit 92 in order to prevent alarge current from rapidly flowing into the capacitive component that ispresent in the first load 94.

The control unit 88 is configured to repeatedly execute the prechargecontrol shown in FIG. 3 , and determines whether a predeterminedprecharge condition is fulfilled in accordance with the start of theprecharge control in FIG. 3 . The precharge condition may be that “theswitch unit 98 (e.g., ignition switch) is switched from the OFF state tothe ON state”, for example, but may also be another predeterminedcondition.

Upon determining that the precharge condition is fulfilled in step S1,in step S2, the control unit 88 causes the second voltage conversionunit 22 to start the second voltage conversion operation. The secondvoltage conversion operation is an operation in which the second voltageconversion unit 22 lowers the voltage applied to the input sideconductive path 12A of the second conductive path 12 and applies theresultant voltage to the output side conductive path 12B in accordancewith the control signal supplied from the outside. Specifically, thesecond voltage conversion operation is realized as follows.

Upon starting the second voltage conversion operation in step S2, instep S3, the control unit 88 determines whether the switching conditionhas been fulfilled. Specifically, in step S3, the control unit 88determines whether the voltage of the first conductive path 10 isgreater than or equal to a predetermined threshold based on the detectedvalue of the first voltage detection unit 80. If the voltage of thefirst conductive path 10 is less than or equal to the predeterminedthreshold, the processing moves to “No” in step S3, and if the voltageof the first conductive path 10 is greater than or equal to thepredetermined threshold, the processing moves to “Yes” in step S3, andin step S4, shifts from the second voltage conversion operation to athird voltage conversion operation.

Furthermore, the control unit 88 determines the duty ratio based on thedetected value of the first voltage detection unit 80 or the firstcurrent detection unit 84, and generates the PWM signal SG2 with thedetermined duty ratio. Thereafter, the control unit 88 outputs the PWMsignal SG2 to the second drive unit 32. Upon receiving the input of thisPWM signal SG2, the second drive unit 32 outputs the control signal withthe duty ratio of the PWM signal SG2 to one switching element 24A of thereverse-flow prevention switching elements 24, and outputs, to theswitching element 28, the PWM signal that is complementary to thiscontrol signal. In other words, a synchronous rectification-type controlin which the switching element 28 is turned OFF when the switchingelement 24A is turned ON, and the switching element 28 is turned ON whenthe switching element 24A is turned OFF, is executed, while also settinga dead time. The control signal from the second drive unit 32 is inputto the signal generation circuit 34 as well. When the signal SG3 is aninterruption instruction signal, the signal generation circuit 34outputs the OFF signal to the switching elements 24B and 24C, and atthis time, the switching elements 24B and 24C are brought into the OFFstate. Also, when the signal SG3 is a permission signal, the signalgeneration circuit 34 outputs, to the switching elements 24B and 24C, asignal that is the same as the signal output to the gate of theswitching element 24A from the second drive unit 32. While causing thesecond voltage conversion unit 22 to perform the second voltageconversion operation (during the output of the control signal to thegate of the switching element 24A), the control unit 88 sets the signalSG3 that is input to the signal generation circuit 34 to theinterruption instruction signal, and thus the switching elements 24B and24C are kept in the OFF state while the second voltage conversion unit22 performs the second voltage conversion operation. In other words,during the second voltage conversion unit 22 performing the secondvoltage conversion operation, the control signal output from the seconddrive unit 32 is output to only the switching element 24A, and theswitching elements 24B and 24C are kept in the OFF state. Accordingly,only the switching element 24A is turned ON/OFF.

In this manner, due to the PWM signal (control signal) being supplied tothe switching element 24A from the second drive unit 32, the secondvoltage conversion unit 22 performs the second voltage conversionoperation so that the voltage applied to the input-side conductive path12A is lowered and the resultant voltage is applied to the output-sideconductive path 12B. In this second voltage conversion operation,control is performed so that the feedback operation for calculating theduty ratio is repeated so that the voltage applied to the firstconductive path 10 approximates a desired target voltage that is lowerthan the output voltage when the second power supply unit 92 is fullycharged, and the voltage applied to the first conductive path 10approximates the desired target voltage. Note that the control unit 88may also control the duty ratio of the PWM signal supplied to theswitching element 24A while monitoring the current flowing through thefirst conductive path 10 so that the current flowing through the firstconductive path 10 during the second voltage conversion operation isconstant. While the second voltage conversion operation is performed inthis manner, the capacitive component of the first load 94 is charged.Note that although the plurality of switching elements 42 are kept inthe OFF state during the second voltage conversion operation, theswitching elements 40 may also be kept in the ON state while suppressinga loss, or the switching element 40 may also be kept in the OFF state.

If it is determined that the predetermined switching condition isfulfilled in step S3, in other words, if it is determined that thevoltage of the first conductive path 10 is greater than or equal to thepredetermined threshold, in step S4, the control unit 88 ends the secondvoltage conversion operation by the second voltage conversion unit 22,and starts the third voltage conversion operation by the first voltageconversion unit 21. The third voltage conversion operation is anoperation in which a synchronous rectification-type boost operation isperformed in the voltage conversion device 20 by supplying an ON signalbased on the PWM signal SG1 to the switching elements 40 and 42alternately from the first drive unit 50, and the voltage applied to thesecond conductive path 12 is boosted and applied to the first conductivepath 10.

During this third voltage conversion operation, the control unit 88stops the output of the interruption instruction signal SG3 to thesignal generation circuit 34, and outputs the ON signal to the seconddrive unit 32. Upon receiving the input of this ON signal, the seconddrive unit 32 outputs the ON signal to all the switching elements 24A,24B, 24C . . . and so on constituting the reverse-flow preventionswitching element 24, and outputs the OFF signal to the switchingelement 28. Accordingly, during the third voltage conversion operation,all the switching elements 24A, 24B, 24C . . . and so on constitutingthe reverse-flow prevention switching element 24 are kept in the ONstate, and the switching element 28 is kept in the OFF state.

The control unit 88 determines the duty ratio based on the valuedetected by the first voltage detection unit 80 or the first currentdetection unit 84, and generates a PWM signal SG1 with the determinedduty ratio. Specifically, the control unit 88 performs control so thatthe feedback operation for calculating the duty ratio is repeated sothat the voltage applied to the first conductive path 10 approximates adesired target voltage that is higher than the output voltage when thesecond power supply unit 92 is fully charged, and the voltage applied tothe first conductive path 10 approximates the desired target voltage.The control unit 88 outputs the thus generated PWM signal SG1 to onlythe first drive unit 50 corresponding to the one first voltageconvention unit 21 of the plurality of first voltage conversion units21. Upon receiving the input of this PWM signal SG1, the first driveunit 50 outputs, to the switching element 42, a control signal (thirdcontrol signal) with the duty ratio of the PWM signal SG1, and outputs,to the switching element 40, a control signal that is complementary tothis control signal (PWM signal SG1). In other words, a synchronousrectification-type control is executed so that the switching element 40is turned OFF when the switching element 42 is turned ON, and theswitching element 40 is turned ON when the switching element 42 isturned OFF, while setting a dead time. Note that the control unit 88outputs an OFF signal to the first drive units 50 of the other firstvoltage conversion units 21 (the first voltage conversion units 21 thatdo not receive the input of the PWM signal) of the plurality of firstvoltage conversion units 21. Upon receiving the input of the OFF signal,the first drive units 50 keep the corresponding switching elements 40and 42 in the OFF state.

In this manner, the third voltage conversion operation, in which thevoltage applied to the second conductive path 12 is boosted and appliedto the first conductive path 10, is performed. In this third voltageconversion operation, it is possible to further accumulate electriccharge in the capacitive component of the first load 94 in which theelectric charge has been accumulated by the second voltage conversionoperation, and further increase the charge voltage of the capacitivecomponent.

Upon starting the third voltage conversion operation in step S4, in stepS5, the control unit 88 determines whether a predetermined precharge endcondition is fulfilled. The predetermined precharge end condition is,for example, that “the voltage of the first conductive path 10 hasexceeded a predetermined voltage”, or the like.

If it is determined that the precharge end condition has not beenfulfilled in step S5, the control unit 88 repeats step S5 until theprecharge end condition is fulfilled. During this period, the chargingof the capacitive component of the first load 94 progresses. If it isdetermined that the precharge end condition has been fulfilled in stepS5, in step S6, the control unit 88 ends the third voltage conversionoperation. In other words, the control unit 88 stops the outputs of thePWM signal SG1, the PWM signal SG2, the interruption instruction signalSG3, and the boost instruction signal SG4. Accordingly, precharging thefirst load 94 is complete.

Upon ending the third voltage conversion operation in step S6, thecontrol unit 88 switches the switch unit 98 from the OFF state to the ONstate, for example. In this way, it is possible to switch the switchunit 98 to the ON state in the state where the capacitive component ofthe first load 94 has been charged to some extent, and thus a situationwhere a large current flows into the capacitive component of the firstload 94 is not likely to occur. After switching the switch unit 98 tothe ON state in accordance with step S6, the control unit 88 mayfunction so that the voltage conversion device 20 performs theabove-described voltage drop operation to lower the voltage applied tothe first conductive path 10 and apply the output voltage to the secondconductive path 12.

Note that in this configuration, the control unit 88 outputs the boostinstruction signal SG4 to the voltage generation unit 66 during thefirst voltage conversion operation, the second voltage conversionoperation, or the third voltage conversion operation. During the periodin which this boost instruction signal SG4 is supplied, the voltagegeneration unit 66 boosts the input voltage (voltage applied to thesecond conductive path 12) and outputs the resultant voltage to theanode side of the diode 64. Note that the control unit 88 may alsooutput the boost instruction signal SG4 in any or all of the periods,namely, during the first voltage conversion operation, the secondvoltage conversion operation, and the third voltage conversionoperation. The control unit 88 may also output the boost instructionsignal SG4 only when the voltage applied to the second conductive path12 is less than or equal to a predetermined value.

Next, the effects of the power supply device 1 will be illustrated.

The above-described power supply device 1 can cause the second voltageconversion unit 22 to perform the second voltage conversion operation inaccordance with a predetermined precharge condition being fulfilled.Accordingly, if it is possible to switch the switch unit 98 from the OFFstate to the ON state at least after performing the second voltageconversion operation in this manner, the switch unit 98 is switched fromthe OFF state to the ON state in a state where charging of thecapacitive component has progressed to some extent. As a result, it ispossible to suppress the inrush current that flows into the capacitivecomponent from the first power supply unit 90 immediately after theswitching.

Furthermore, when a predetermined switching condition has been fulfilledin the second voltage conversion operation, the third voltage conversionoperation can be performed such that the voltage applied to the secondconductive path 12 is boosted and the resultant voltage is applied tothe first conductive path 10, making it possible to further charge thecapacitive component connected to the first conductive path 10 side.

Furthermore, with this configuration, when the control unit 88 causesthe first voltage conversion unit 21 to perform the third voltageconversion operation in accordance with a predetermined switchingcondition being fulfilled, only some of the semiconductor switchingelements 21 of the plurality of the semiconductor switching elements 21are supplied with the third control signal, whereby only some of thefirst voltage conversion units 21 are caused to perform the thirdvoltage conversion operation. Accordingly, it is possible to reduce thepower that is required for the control unit 88 to drive the firstvoltage conversion unit 21 during the third voltage conversionoperation. Accordingly, even if the voltage of the power supply thatsupplies power to the control unit 88 drops, a situation where thecontrol unit 88 cannot perform the control of the precharge operation(control of the third voltage conversion operation) is not likely tooccur.

Furthermore, the power supply device 1 is provided with the plurality ofthird conductive paths 60 that serve as the power supply path from thesecond conductive path 12 to the control unit 88. The plurality of thirdconductive paths 60 are connected in parallel with each other betweenthe second conductive path 12 and the control unit 88, and one of thethird conductive paths 60 is provided with the voltage generation unit66 that boosts the voltage applied to the conductive path on the secondconductive path 12 side and applies the output voltage to the conductivepath on the control unit 88 side. With this configuration, even if thevoltage applied to the second conductive path 12 is small, the voltagegeneration unit 66 can boost the voltage applied to the conductive pathon the second conductive path 12 side and apply the output voltage tothe conductive path on the control unit 88 side. Accordingly, even ifthe voltage applied to the second conductive path 12 is small, the drivevoltage required for the operation of the control unit 88 is likely tobe ensured.

Furthermore, upon starting the second voltage conversion operation, thecontrol unit 88 supplies the third control signal to the one firstvoltage conversion unit 21 of the plurality of the first voltageconversion units 21 to cause only one first voltage conversion unit 21to perform the third voltage conversion operation. With thisconfiguration, it is possible to further reduce the “power required forthe control unit 88 to drive the first voltage conversion unit 21 duringthe third voltage conversion operation”. Accordingly, even if thevoltage of the power supply that supplies power to the control unit 88drops, a situation where the control unit 88 cannot perform control ofthe precharge operation (control of the third voltage conversionoperation) is less likely to occur.

OTHER EMBODIMENTS

The present disclosure is not limited to the embodiment illustratedbased on the above descriptions and the drawings, and the followingembodiments are also included in the technical scope of the presentdisclosure.

In the first embodiment, the control signal is output to only one of thereverse-flow prevention switching elements 24 in the second voltageconversion operation, but a configuration is also possible where thecontrol signal is output to two or more reverse-flow preventionswitching elements 24 as long as it is only a part of the reverse-flowprevention switching elements 24.

In the first embodiment, the voltage generation unit 66 is provided onthe third conductive path 60, but the voltage generation unit 66 mayalso be omitted.

In the first embodiment, the switching element is turned ON in thesecond voltage conversion operation, but the switching element 40 mayalso be turned OFF. In this case, the current flows toward the firstload 94 via the body diode of the switching element 40.

In the first embodiment, in the third voltage conversion operation, thecontrol signal is output to the switching element 40 and 42 of one ofthe plurality of first voltage conversion units 21, but the controlsignal may also be output to the switching elements 40 and 42 of two ormore of the first voltage conversion units 21 as long as it is theswitching elements 40 and 42 of only a part of the first voltageconversion units 21.

Although the semiconductor element part is the switching element in thefirst embodiment, the semiconductor element part may also be a diode. Ifthe semiconductor element part is a diode, a configuration is possiblein which the anode is electrically connected to the reference conductivepath, the cathode is electrically connected between the second inductor26 and the reverse-flow prevention switching element 24 on the secondconductive path 12, and the second voltage conversion unit 22 functionsas a diode-type DC-DC convertor.

The invention claimed is:
 1. An in-vehicle power supply deviceconfigured to lower a voltage applied to a first conductive path that iselectrically connected to a capacitive component and apply the resultantvoltage to a second conductive path, or boost a voltage applied to thesecond conductive path and apply the resultant voltage to the firstconductive path, the in-vehicle power supply device comprising: a firstvoltage conversion unit that includes a first drive switching element, asecond drive switching element, and a first inductor, performs a firstvoltage conversion operation in which a voltage applied to the firstconductive path is lowered and an output voltage is applied to thesecond conductive path, in accordance with a first control signal, inwhich an ON signal and an OFF signal are alternately switched, beingsupplied to the first drive switching element, and performs a thirdvoltage conversion operation in which a voltage applied to the secondconductive path is boosted and an output voltage is applied to the firstconductive path in accordance with a third control signal, in which anON signal and an OFF signal are alternately switched, being supplied tothe second driving switching element; a reverse-flow preventionswitching element that is provided on the second conductive path andthat interrupts a flow of a current on the second conductive path towardthe first voltage conversion unit when turned OFF; a second inductorthat is provided between the first voltage conversion unit and thereverse-flow prevention switching element on the second conductive path,and in series with respect to the reverse-flow prevention switchingelement; a semiconductor element part constituted by a diode or aswitching element that has one end electrically connected to the secondinductor and the reverse-flow prevention switching element on the secondconductive path and another end electrically connected to a referenceconductive path; and a control unit that outputs the first controlsignal to at least the first drive switching element, and outputs thethird control signal to the second drive switching element, wherein aplurality of the first voltage conversion units are connected inparallel with each other between the first conductive path and thesecond conductive path, a second voltage conversion unit is configuredby including the reverse-flow prevention switching element, the secondinductor, and the semiconductor element part, and, when a part of thesecond conductive path that is on the first voltage conversion unit sideof the second voltage conversion unit is regarded as an output-sideconductive path, and a part of the second conductive path that is on theside opposite to the first voltage conversion unit side is regarded asan input-side conductive-path, the second voltage conversion unitperforms the second voltage conversion operation in which the voltageapplied to the input-side conductive path is lowered, and an outputvoltage is applied to the output-side conductive path, the control unitbeing configured to cause the second voltage conversion unit to performthe second voltage conversion operation in accordance with apredetermined precharge condition being satisfied, by applying a secondcontrol signal, in which an ON signal and an OFF signal are alternatelyswitched, to the reverse-flow prevention switching element, and uponstarting the second voltage conversion operation, the control unitsupplies the third control signal to only some of the plurality of thefirst voltage conversion units in accordance with a predeterminedswitching condition being fulfilled, thereby causing some of the firstvoltage conversion units to perform the third voltage conversionoperation.
 2. The in-vehicle power supply device according to claim 1,comprising: a plurality of third conductive paths that serve as a powersupply path from the second conductive path to the control unit, whereinthe plurality of third conductive paths are connected in parallel witheach other between the second conductive path and the control unit, anda voltage generation unit that boosts a voltage applied to theconductive path on the second conductive path side and applies theoutput voltage to the conductive path on the control unit side isprovided on one of the third conductive paths.
 3. The in-vehicle powersupply device according to claim 1, wherein upon starting the secondvoltage conversion operation, the control unit supplies the thirdcontrol signal to only one first voltage conversion unit of theplurality of first voltage conversion units in accordance with apredetermined switching condition being fulfilled, thereby causing theone first voltage conversion unit to perform the third voltageconversion operation.
 4. The in-vehicle power supply device according toclaim 2, wherein upon starting the second voltage conversion operation,the control unit supplies the third control signal to only one firstvoltage conversion unit of the plurality of first voltage conversionunits in accordance with a predetermined switching condition beingfulfilled, thereby causing the one first voltage conversion unit toperform the third voltage conversion operation.